Complex spatio-temporal structure of the Holocene Thermal Maximum

Analysis of the largest available database of Holocene temperature time series covering past 12,000 years reveals complex spatio-temporal trends and challenges the paradigm of a globally synchronous Holocene Thermal Maximum. Inconsistencies between Holocene climate reconstructions and numerical model simulations question the robustness of climate models and proxy temperature records. Climate reconstructions suggest an early-middle Holocene Thermal Maximum (HTM) followed by gradual cooling, whereas climate models indicate continuous warming. This discrepancy either implies seasonal biases in proxy-based climate reconstructions, or that the climate model sensitivity to forcings and feedbacks needs to be reevaluated. Here, we analyze a global database of Holocene paleotemperature records to investigate the spatiotemporal structure of the HTM. Continental proxy records at mid and high latitudes of the Northern Hemisphere portray a "classic" HTM (8-4 ka). In contrast, marine proxy records from the same latitudes reveal an earlier HTM (11-7ka), while a clear temperature anomaly is missing in the tropics. The results indicate a heterogeneous response to climate forcing and highlight the lack of globally synchronous HTM.